Maybe not a leak so much as a bypass and resulting unfed bearing, and subsequent catastrophic failure mode that happens quicker than the temp change can be or gets sensed.
Then, the sensors would pick up nothing if each bearing is not monitored (which I would do).
There are many places oil can leak, inside and outside the engine, and there have been cases where oil loss has gone unnoticed in flight. Turbine bearing seal failure blows oil out the exhaust with barely detectable increase in smoke and no measurable effect on temperature. Bearing failure happens fast once lube spray (cooling!) is lost; possibly faster that pilot reaction to an alarm. Automatic shutdowns risk shutting down an engine for a sensor failure, and sometimes it could be better to continue running a damaged engine and risk total engine failure than to certainly crash.
But indeed something was screwed up, the details will be figured out and the problem fixed. Not unusual with a new engine design.
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